Semiconductor processing, including cleaning and polishing of a substrate as well as deposition of films on the substrate, is one application where it is desirable to hold an article and rotate the article about an axis perpendicular to a surface of the article. Often, it is desirable to exert considerable control over the rotation of the article as well as the relative angular position of the article when the rotation of the article is interrupted.
One type of rotational support includes a vacuum chuck which is rotated by a complex drive system including belts, pulleys and a motor for driving the rotation of the chuck as well as a tensioning device for maintaining a generally constant belt tension during operation. This type of support occupies considerable space and requires frequent maintenance, including adjustment of the drive components and inspection and replacement of the belt, to ensure the rotation support is operating properly. U.S. Pat. No. 5,374,315 discloses an example of a rotational support mechanism for use in chemical vapor deposition equipment. The disclosed device includes a variable speed DC motor and a drive belt which is mounted between a pair of drive pulleys to transmit rotary power from the motor to a drive shaft coupled to the substrate support. A purge gas is fed through the shaft to the area of the substrate support.
While complex drive systems including belts and pulleys may be used to rotate a chuck or other support assembly and change the angular position of the substrate retained thereon, minimizing the components of a rotational support offers the advantages of reducing the amount of space occupied by the equipment as well as the number of maintenance and timing adjustments which are required. For those applications requiring strict control over the rotation and angular position of the substrate, a rotational support system which improves the degree of control over the rotation and position of the substrate as well as the consistency of the drive system over an extended period of time is desirable. Improving control over rotation while minimizing interruptions for maintenance, repair and the like would significantly enhance the efficiency of the operation utilizing the rotational support system.